Common mode signal emitter coupling differential amplifier circuit a

Common mode signal emitter coupling differential amplifier circuit a

Assume that signals of equal size and polarity (called common mode signals) are added to the two input terminals of the circuit, as shown in Figure (a), then
the seven I and R will increase at the same time, so that the current flowing through Ie = ICI +ICZ. As a result, the potential U at point e increases, which acts as a negative current feedback. In other
words, for the common-mode input signal , the existence of & introduces strong negative feedback, which greatly reduces the common-mode amplification factor, thus reducing the zero-
point drift.
    Figure (b) shows an application example of a differential amplifier in an audio power amplification circuit. Two sets of differential amplifiers are used in the input circuit
. This effectively suppresses the generation of zero point drift and reduces the impact of noise and interference.